From 1235f504aaba2ebeabc863fdb3ceac764a317d47 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Mon, 26 Jul 2010 13:09:16 -0700 Subject: [PATCH] netlink: netlink_recvmsg() fix commit 1dacc76d0014 (net/compat/wext: send different messages to compat tasks) introduced a race condition on netlink, in case MSG_PEEK is used. An skb given by skb_recv_datagram() might be shared, we must copy it before any modification, or risk fatal corruption. Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- net/netlink/af_netlink.c | 22 ++++++++++++++++------ 1 file changed, 16 insertions(+), 6 deletions(-) diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c index 8648a9922aab..2cbf380377d5 100644 --- a/net/netlink/af_netlink.c +++ b/net/netlink/af_netlink.c @@ -1406,7 +1406,7 @@ static int netlink_recvmsg(struct kiocb *kiocb, struct socket *sock, struct netlink_sock *nlk = nlk_sk(sk); int noblock = flags&MSG_DONTWAIT; size_t copied; - struct sk_buff *skb, *frag __maybe_unused = NULL; + struct sk_buff *skb; int err; if (flags&MSG_OOB) @@ -1441,7 +1441,21 @@ static int netlink_recvmsg(struct kiocb *kiocb, struct socket *sock, kfree_skb(skb); skb = compskb; } else { - frag = skb_shinfo(skb)->frag_list; + /* + * Before setting frag_list to NULL, we must get a + * private copy of skb if shared (because of MSG_PEEK) + */ + if (skb_shared(skb)) { + struct sk_buff *nskb; + + nskb = pskb_copy(skb, GFP_KERNEL); + kfree_skb(skb); + skb = nskb; + err = -ENOMEM; + if (!skb) + goto out; + } + kfree_skb(skb_shinfo(skb)->frag_list); skb_shinfo(skb)->frag_list = NULL; } } @@ -1478,10 +1492,6 @@ static int netlink_recvmsg(struct kiocb *kiocb, struct socket *sock, if (flags & MSG_TRUNC) copied = skb->len; -#ifdef CONFIG_COMPAT_NETLINK_MESSAGES - skb_shinfo(skb)->frag_list = frag; -#endif - skb_free_datagram(sk, skb); if (nlk->cb && atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf / 2) -- 2.39.5